The present invention relates to a lignosulfonate - urea - formaldehyde composition, its use and its preparation.
Lignosulfonate (LS) commonly is used as a generic term for spent sulfite liquor (SSL), LS purified from SSL, sulfonated alkali lignin from alkaline pulping processes, e.g. Kraft Process, and sulfonated hydrolysis lignin obtained from wood saccharification. For the purposes of this invention LS refers to SSL or LS purified from SSL.
LS is obtained from the sulfite pulping process in which wood is cooked with sulfite at elevated temperatures at or below pH 7. In this process the lignin, about 25% of wood, is partially hydrolyzed and sulfonated, and is rendered water soluble. Hemicelluloses are also partially hydrolyzed to reducing sugars and oligosaccharides. The cellulose, approximately the remaining 50% of wood, is left largely intact and insoluble. It is removed leaving soluble LS in solution or more specifically SSL.
SSL, as is, at 8-15% solids, or concentrated, or fractionated, or dried is used commercially in many application areas, for example in dispersion and binding.
LS is used to provide higher green and dried strengths in the manufacture or refractory shapes, face brick, and ceramics. It is used in pelleting of animal feeds to give stronger pellets, less fines development during handling and improved feed consumption and conversion. LS is used to make foundry sand molds. It is used as a binder to granulate various fine substrates in pin mixers, Muller mixers, disk and drum granulators. It is used as a binder in briquetting. LS is coated topically to abate dusting from roads, coal, siliceous materials, other clays, fertilizers and prills.
In these applications, LS adsorbs to surfaces of the substrate, and at correct concentrations can provide tack in the system. Upon drying very strong shapes result. These shapes remain strong as long as they are dry, probably due to extensive hydrogen bonding, since LS contains sulfonic, carboxyl and hydroxyl groups. Water redissolves LS and as a result shapes bound with it will degrade with moisture.
The water solubility of LS has limited its utility. Topical treatments are impermanent, depending upon weather. As a result, various attempts have been made to improve water resistance of LS bound shapes as for example emulsification of hydrophobes in LS, U.S. Pat. No. 4,666,522 by Hollis et al. While the hydrophobe inclusion substantially delays the access of moisture to LS bonds, especially in compacted shapes, the LS is eventually accessible to water and the bonds broken.
On the other hand, for many years phenolformaldehyde resins (PF) and urea-formaldehyde resins (UF) have been used to generate highly water resistant and moderately water resistant bonds, Handbook of Adhesives by Skeist. Even moderately water resistant UF bonds far exceed resistance obtained by LS because PF and UF actually react to form covalent bonds.
Because of the economy of using LS verus UF and PF, there are reported numerous efforts at extension of resins with LS.
Holmquist H. W., U.S. Pat. No. 4,186,242 reports hot pressing of wood chips with UF and ammonium lignosulfonate to get reduced formaldehyde emissions, the UF and ammonium lignosulfonate being added separately. Doronin, Yu G et al, Derevoobrah, Prom-st. 1983(3) 11-13 reports that addition of LS at&lt;20% to UF did not adversely affect physico-mechanical properties of hardboard but resulted in decreased water resistance. When LS was added to the resin rather than separately, water miscibility was decreased. Svitkina, M. M. et al, Derevoobrah Prom-st. 1982(4) 4-6 report that adding 15% and 10% LS to surface and middle layers respectively, along with UF, gave good particle board. However, mixing 750-800 kg LS with 25 tons binder at 30.degree.-35.degree. C. gave increased resin viscosity and decreased miscibility to resin with water. Coyle R. P., U.S. Pat. No. 3,931,072 cites alkaline methylolation of LS with formaldehyde and then phenol and more formaldehyde to make a LS - PF resol resin. Bornstein, U.S. Pat. No. 4,130,515 reports an LS-melamine-formaldehyde board binder made by reacting the components in-situ under alkaline conditions. Tomis, B. et al, Czech Patent No. 202,450 reports a water resistant binder from a two step condensation, first condensing 2:1 moles of formaldehyde: urea at pH 7 -pH 9.5, reducing pH to 5.1 with formic acid and condensing additionally with LS, LS being about 10% of the final binder solids. Morze et al, Zb. Ref-Semin. "Pokroky Vyrobe Pouziti Lepidiel Drevopriem" 6:112-121, 1983 showed addition of Calcium LS to UF decreased formaldehyde release but caused deterioration of particle board properties. They recommended a maximum extension of UF to be 20%. In U.S. Pat. No. 3,990,928 Grabowsky shows that addition of small amounts of sodium lignosulfonate improves the cold adhesion of glue UF to wood particles. Azorou, V. I. et al, Soviet Patent No. 1,237,678 makes an alkali lignin UF resin by premethylolation of alkali lignin at pH 9-2, adds urea and condenses at pH 7.5-9.0 and finally adds NH.sub.4 Cl reducing pH to 5.0-6.5 to further condense and reduce free formaldehyde level. Resin cure was faster and storage time went from 2-3 months to 4-7 months. The highest level of alkali lignin obtained in resin was 17% of solids.
Edler, F. J., U.S. Pat. No. 4,194,997 and U.S. Pat. No. 4,244,846 relates a significant achievement in mixing UF resins and LS. Significant is the fact that Edler reports for the first time being able to obtain UF-LS mixtures containing high levels of LS whch are compatible using very low condensed UF resins. That Edler has a mixture rather than a reaction product is evident in that similar reacted formulations are not compatible and that low solids precipitates UF.
Thiel et al, U.S. Pat. No. 3,994,850 reports a stable resin including 5% to 30% LS by reacting urea and formaldehyde in the presence of lignosulfonates. Keim G. I., U.S. Pat. No. 2,622,979 reports a high strength paper container treated with a LS modified UF resin in which the resin contains 5% to 20% LS on urea. Maier, C. et al, Romanian Patent No. 89,056 reports a three step condensation of formaldehyde with urea, adding 5% to 30% sodium LS in the final polycondensation step.
Krut-ko N. P. et al, Z. Prikl. Spektr. 48(1) 95-98, 1988 studied the reaction of mixtures by infrared spectroscopy. They report evidence that reaction occurs between the sulfo and carbonyl groups of sodium LS giving crosslinking. The effect was intensified by heating.
None of the adhesive or resin work has been able to provide a reacted LS-urea-formaldehyde resin including large amounts of LS, in fact not more than 20%. Furthermore, UF resins typically contain 40% -45% free formaldehyde, less if diluted, which is in itself a hazardous chemical, i.e. a carcinogen. These resins must be handled and used carefully.
The present invention relates to a novel and improved LS-urea-formaldehyde composition, its use and to a method for producing such composition. The invention is a non-toxic, stable composition including in solution about 55 to 95 parts methylol lignosulfonate - urea - formaldehyde polymer, about 1-28 parts sugars, and about 1-30 parts oligosaccharides and a free formaldehyde content of less than 1% on solids. The invention resin is non-toxic to rats, LD.sub.50 &gt;5 gm/kg body weight, and is non-irritating to skin and eyes. The invention resin is a stable solution for at least two months. It is easily spray dried to provide a powder which can be incorporated as an adhesive or reconstituted to 50% solution.
It is an object of the invention to provide a composition which is suitable for use in the manufacture of hardboard.
It is another object of the invention to provide a composition which is suitable for use in the preparation of high quality animal feed pellets for aquaculture wherein said pellets have extended survival time in water.
Still another object of the invention is to provide a composition which can coat substrates such as siliceous materials, coal, etc. and cure at ambient temperature to eliminate dusting and provide a waterproof barrier. For example waste sites, coal piles, etc.
Still another object of the invention is to provide a composition which can be used in the manufacture of molds and bricks or other shapes which will be resistant to moisture.
Another object of the invention is to provide a low cost composition which is based in large part on a very low cost waste product, spent sulfite liquor, thereby alleviating environmental problems while providing a unique economical resin composition.
The invention is a stable methylol lignosulfonate - urea - formaldehyde resin preferably including, on a solids basis, about 75 parts calcium methylol lignosulfonate - urea - formaldehyde resin, about 12 parts of reducing sugars, about 5 parts ammonium ion and about 13 parts oligosaccharides.
We have discovered that acidic premethylolation of LS to achieve consumption of about 3% formaldehyde on SSL, about 0.8 methylol groups per monomeric unit of the lignosulfonate portion of the SSL, is essential to produce a stable invention with good performance. Without this step we, as others, find reaction of such a high level of LS with urea and formaldehyde gives insolubles formation and gelling. Accordingly, about 2 to 8 parts formaldehyde is reacted with about 70 parts spent sulfite liquor having a range of from about 45 to 65% total solids to form the acid methylolated lignosulfonate. If is more than about 8 parts formaldehyde is employed there is excess formaldehyde which, during the next succeeding step with urea forms UF resin which reacts with the lignosulfonate to form an undesirable insoluble product. Additionally, if less than about 2 parts formaldehyde is used there is insufficient reaction with the lignosulfonate, i.e. there is insufficient methylolation of a lignosulfonate.
The second step involves reaction with urea at about a 3:1 molar ratio to formaldehyde added for the methylolation. The urea-rich reaction provides a chemical environment for reaction of urea with the methylol groups of the methylol-rich LS. Accordingly, about 10 to 30 parts urea on spent sulfite liquor solids is employed. If more than about 23 parts are utilized, an undesirable insoluble product is formed. If less than about 10 parts urea is employed, there is insufficient reaction to obtain the lignosulfonate methylene urea.
After formation of mainly lignosulfonate methylene urea, additional formaldehyde is added to give a total added formaldehyde to urea ratio of about 2.6:1 and further condensation is conducted. If the formaldehyde in this step is added with urea in the prior step, an insoluble gelling composition results because urea preferentially reacts with the formaldehyde rather than the methylol lignosulfonate to form UF in the presence of the lignosulfonate. The UF reacts during heating with the LS to form a high level of insolubles. Accordingly, about 16 to 25 parts formaldehyde is employed in this subsequent formaldehyde reaction with the lignosulfonate methylene urea. Less than about 16 parts results in undesirable insolubles while more than about 25 parts results in excess formaldehyde which is toxic and thus undesirable. As noted above, the total molarity of the formaldehyde to urea in the system is about 2.6 moles of formaldehyde per mole of urea. If less than about 2.4 moles of formaldehyde per mole of urea in the system is employed, the system gells up resulting in undesirable insoluble compounds. As a result, there must be at least a total molarity of about 2.4 or higher in the system in order to properly form the methylol lignosulfonate urea formaldehyde polymer.
Finally, about 6% ammonia on total solids may be added if desired to give pH 7.5-9.0 for the final liquid which is stable for about two months and which can be easily spray dried to a powder. That the chosen amount of ammonia addition gives the desired pH is significant as a measure of desired completion of the final reaction of formaldehyde. If reaction is not completed, the pH will be less than the desired level due to formation of excessive hexamethylenetetramine. Accordingly, about 5 to 8 parts ammonia gives the desired pH to quench the reaction and provide stability therefore. Although ammonia is preferable, any compound or mixture of compounds that raises the pH to between 7.5 to 9.0 may be employed so long as that compound also results in tying up any excess formaldehyde in the system.
The significance of acid methylolation for the solubility and stability is great. For example, as reported herein, Azarov VI et al premethylolated alkali lignin under alkaline conditions but did not achieve a product of high lignin content. In alkali or Kraft lignin about one-third of the phenolic nuclei are free in the 5-position ortho to the phenolic hydroxy, Marton J. et al Lignin Structure and Reactions, 1966 pp. 125-144. Therefore, methylolation is limited to about 0.33 methylol groups per lignin monomer. In acid methylolation, reaction is preferentially at the site meta to phenolic hydroxyl. There are many more of these sites available and, unlike alkaline catalyzed methylolation, the significance of whether or not the phenolic group is free or involved in a linkage with another monomer disappears. A free phenolic group allows reaction to proceed more easily in alkaline reaction with formaldehyde. That a higher level of methylolation, 0.8/monomer, achieved by the invention allows essentially all of the UF condensate (polymethylene urea) to be attached to the more hydrophillic calcium lignosulfonate providing the desired solubility characteristics.
Isolation of the active resinous component of the composition shows intact sulfo groups and equivalent calcium indicating non-involvement of sulfo groups which Krut-ko et al showed to be involved in reaction when UF resin was mixed and reacted with lignosulfonate such as in the Edler mixtures of UF and SSL.
Furthermore, the composition includes essentially all of the urea reacted with the methylol lignosulfonate.
Clearly there are advantages over prior art in addition to novelty. The invention is non-toxic. The invention can be used widely because there is no dangerous evolution of formaldehyde in unprotected environments. The invention gives bonding of wood particles when used at concentrations of about 1-5% by weight that is essentially equal to that bond quality obtained with PF resin, and a bond far more water resistant than obtainable with UF resin. The invention can be used at a concentration of about 0.5-4% by weight for pelleting animal feeds while PF and UF resins cannot because of toxicity and/or adverse effects on feed utilization and animal growth. The invention based upon waste sulfite liquor can be spread at a concentration of about 0.3-3 gal./yd..sup.2 to dry and cure as a water impervious film at ambient temperatures. Also, when used in concentrations of about 1-5% by weight, as an additive in the manufacture of refractory materials provides water resistant dry shapes which are not appreciably degraded by moisture. For example, the invention is useful in the manufacture of refractory brick and/or ceramics.